Composite cathode active material, method of preparing the composite cathode active material, and cathode and lithium battery each including the composite cathode active material

ABSTRACT

A composite cathode active material, a method of preparing the composite cathode active material, a cathode including the composite cathode active material, and a lithium battery including the cathode. The composite cathode active material includes a lithium intercalatable material; and a garnet oxide, wherein an amount of the garnet oxide is about 1.9 wt % or less, based on a total weight of the composite cathode active material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of Korean PatentApplication No. 10-2013-0072720, filed on Jun. 24, 2013, and all thebenefits accruing therefrom under 35 U.S.C. §119, the content of whichis incorporated herein in its entirety by reference.

BACKGROUND

1. Field

The present disclosure relates to a composite cathode active material,methods of preparing the composite cathode active material, and acathode and a lithium battery, each including the composite cathodeactive material.

2. Description of the Related Art

For small and high-performance devices, high energy density is adesirable factor for lithium batteries, in addition to small-size andlight-weight characteristics. High-voltage and high-capacity lithiumbatteries are increasingly desirable.

To provide an improved lithium battery, research into cathode activematerials having a high voltage, excellent high-rate characteristics,and improved lifespan characteristics is being performed.

Available high-voltage cathode active materials cause side reactionswith an electrolyte during charge and discharge, and lead to theproduction of by-products, such as free transition metal or a gas. Dueto the side reaction of cathode active materials and the by-productsgenerated from the cathode active materials, high-rate characteristicsand lifespan characteristics of batteries may be degraded.

Accordingly, there is a need to develop a method of preventing thedeterioration in performance of batteries including high-voltage cathodeactive materials.

SUMMARY

Provided is a composite cathode active material that has high voltageand prevents deterioration in the performance of a battery including thecomposite cathode active material.

Provided is a cathode including the composite cathode active material.

Provided is a lithium battery including the cathode.

Another aspect provides methods of preparing the composite cathodeactive material.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description.

According to an aspect, a composite cathode active material includes: alithium intercalatable material; and a garnet oxide, wherein an amountof the garnet oxide is about 1.9 weight percent (wt %) or less, based ona total weight of the composite cathode active material.

According to another aspect, a cathode includes the composite cathodeactive material.

According to another aspect, a lithium battery includes the cathode.

According to another aspect, disclosed is a method of preparing acomposite cathode active material, the method including: forming a shellincluding contacting a lithium intercalatable material and a garnetoxide to form a shell including the garnet oxide on a core including thelithium intercalatable material to prepare the composite cathode activematerial.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1A is a scanning electron microscopic (“SEM”) image of a compositecathode active material prepared according to Example 1;

FIGS. 1B and 1C are each alternative views of the composite cathodeactive material prepared according to Example 1;

FIG. 2 is a graph of intensity (arbitrary units) versus diffractionangle (2 theta, degrees) and is an X-ray diffraction (“XRD”) spectrum ofa garnet-type oxide prepared according to Preparation Example 1;

FIG. 3A is a graph of intensity (arbitrary units) versus acquisitiontime (seconds, s) which shows a time-of-flight secondary ion massspectrometry (“ToF-SIMS”) spectrum of LaO included in the compositecathode active materials prepared according to Examples 1 to 3 andComparative Examples 1 and 3;

FIG. 3B is a graph of intensity (arbitrary units) versus acquisitiontime (seconds, s) which shows a ToF-SIMS spectrum of a composite cathodeactive material prepared according to Comparative Example 3;

FIG. 3C is a graph of intensity (arbitrary units) versus acquisitiontime (seconds, s) which shows a ToF-SIMS spectrum of a composite cathodeactive material prepared according to Example 3;

FIG. 3D is a graph of intensity (arbitrary units) versus acquisitiontime (seconds, s) showing which shows a ToF-SIMS spectrum of a compositecathode active material prepared according to Example 2;

FIG. 3E is a graph of intensity (arbitrary units) versus acquisitiontime (seconds, s) which shows a ToF-SIMS spectrum of a composite cathodeactive material prepared according to Example 1;

FIG. 3F is a graph of intensity (arbitrary units) versus acquisitiontime (seconds, s) which shows a ToF-SIMS spectrum of a composite cathodeactive material prepared according to Comparative Example 1;

FIG. 4 is a graph of capacity retention (percent) versus number ofcycles (cycle number) which shows lifespan characteristics of lithiumbatteries manufactured according to Examples 25 to 27 and ComparativeExample 9; and

FIG. 5 is a schematic view of an embodiment of a lithium battery.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to the like elements throughout. In this regard, thepresent embodiments may have different forms and should not be construedas being limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects of the present description. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items. “Or” means “and/or.” Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms “first,” “second,”“third” etc. may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer, or section from another element, component, region, layer, orsection. Thus, “a first element,” “component,” “region,” “layer,” or“section” discussed below could be termed a second element, component,region, layer, or section without departing from the teachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±30%, 20%, 10%, 5% of the stated value.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

“Rare earth” means the fifteen lanthanide elements, i.e., atomic numbers57 to 71, plus scandium and yttrium.

The term “intercalatable” means able to intercalate or deintercalate anion.

Hereinafter, a composite cathode active material, methods of preparingthe composite cathode active material, and a cathode and a lithiumbattery, each including the composite cathode active material, will bedisclosed in further detail.

A composite cathode active material according to an embodiment includesa lithium intercalatable material, and a garnet-type oxide, wherein anamount of the garnet-type oxide is about 1.9 weight percent (wt %) orless, based on the total weight of the composite cathode activematerial.

Since the composite cathode active material includes the garnet-typeoxide, the lithium ion transfer performance of the composite cathodeactive material may be improved and ultimately, performance of a lithiumbattery may be improved.

For example, since the composite cathode active material includes about1.9 wt % or less of the garnet-type oxide, the composite cathode activematerial may have improved high-rate characteristics. When the amount ofthe garnet-type oxide is greater than about 1.9 wt %, the transfer ofelectrons may decrease due to the garnet-type oxide, and thus high-ratecharacteristics may decrease. When a garnet-type oxide is not includedthe composite cathode active material, the transfer of lithium ions alsodecreases, and thus high-rate characteristics may decrease.

For example, the amount of the garnet-type oxide in the compositecathode active material may be greater than 0 to about 1.9 wt %. Forexample, the amount of the garnet-type oxide in the composite cathodeactive material may be greater than 0 to about 1.8 wt %. For example,the amount of the garnet-type oxide in the composite cathode activematerial may be greater than 0 to about 1.7 wt %. For example, theamount of the garnet-type oxide in the composite cathode active materialmay be greater than 0 to about 1.6 wt %. For example, the amount of thegarnet-type oxide in the composite cathode active material may begreater than 0 to about 1.5 wt %. For example, the amount of thegarnet-type oxide in the composite cathode active material may begreater than about 0.01 wt % to about 1.9 wt %, or about 0.1 wt % toabout 1.8 wt %, or about 0.2 wt % to about 1.7 wt %, or about 0.01 wt %to about 1.5 wt %. For example, the amount of the garnet-type oxide inthe composite cathode active material may be greater than about 0.1 wt %to about 1.5 wt %. For example, the amount of the garnet-type oxide inthe composite cathode active material may be greater than about 0.1 wt %to 1.0 about wt %. For example, the amount of the garnet-type oxide inthe composite cathode active material may be greater than about 0.2 wt %to about 1.0 wt %. Within these amount ranges, improved batterycharacteristics may be obtained.

The composite cathode active material comprises a core and a shelldisposed on at least a portion of the core, wherein the core comprisesthe lithium intercalatable material, which enables intercalation anddeintercalation of lithium, and wherein the shell includes a garnet-typeoxide. While not wanting to be bound by theory, it is understood thatsince the composite cathode active material has the core/shellstructure, the core may not directly contact the electrolyte, or directcontact between the core and electrolyte may be reduced, and thus, aside reaction of the core with the electrolyte may be suppressed oreffectively eliminated, the decomposition of the electrolyte at thesurface of the core may be prevented, and elution andre-electrodeposition of metal ions included in the core may beprevented. Accordingly, lifespan characteristics of a lithium batteryincluding the composite cathode active material may be improved.

For example, the shell may completely cover the core to completely blockthe core from an electrolyte. For example, although the shell maycompletely cover the core, due to the presence of pores in at least aportion of the shell, the core may contact an electrolyte through thepores. For example, the shell may incompletely cover the core. Forexample, the shell may be formed in a form of an island on the surfacethe core.

In the composite cathode active material, the shell and the core mayform a mechanochemical bond. The shell may be formed on the core byusing a dry coating method, for example, milling, thus, the core and theshell may form a mechanochemical bond. When the mechanochemical bond isformed, a binding force between the core and the shell may increase, anda denser shell may be obtained. For example, when a core particle and aparticle for forming the shell are simply mixed, the core particle andthe particle for forming the shell in the obtained mixture may have asimple physical bond, such as a Van der Waals bond therebetween.However, for forming the shell, when a particle of a material of thecore and a particle of a material of the shell form a mechanochemicalbond by, for example, a mechanofusion method, a Brunauer-Emmett-Teller(“BET”) specific surface area of the obtained composite may besubstantially reduced compared to a BET specific surface area of thesimple mixture described above.

The garnet-type oxide included in the composite cathode active materialmay be represented by Formula 1:L_(5+x)E₃(Me_(z),M_(2−z))O_(d)  Formula 1wherein L is at least one of a monovalent cation and a bivalent cation,some or all of L is Li, E is a trivalent cation, Me and M are eachindependently a trivalent, a 4-valent, a 5-valent, or a 6-valent cation,0<x≦3, 0≦z≦2, and 0<d≦12, some or all of the O may be substituted withat least one of a 5-valent, a 6-valent, and a 7-valent anion, and someof the E may be substituted with a monovalent cation. For example, when0<x≦2.5, E may be La and M may be Zr.

For example, the garnet-type oxide may be represented by Formula 2:Li_(5+x)La₃(Zr_(z)A_(2−z))O₁₂  Formula 2wherein A is at least one of Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, Ga, orGe, 0<x≦3, and 0≦z≦2.

For example, the garnet-type oxide may be at least one of Li₇La₃Zr₂O₁₂,Li_(6.75)La₃(Zr_(1.75)Nb_(0.25))O₁₂, Li_(7.5)Rb_(0.25)La_(2.75)Zr₂O₁₂,Li₈Rb_(0.5)La_(2.5)Zr₂O₁₂, Li₉RbLa₂Zr₂O₁₂,Li_(7.125)Rb_(0.0625)La_(2.9375)Zr₂O₁₂, Li₆SrLa₂Ta₂O₁₂, orLi_(7.125)K_(0.0625)La_(2.9375)Zr₂O₁₂.

The shell included in the composite cathode active material mayadditionally include a carbonaceous material. Since the shelladditionally includes a carbonaceous material, which can have highelectronic conductivity, electronic conductivity of the shell may beimproved.

For example, the carbonaceous material may comprise at least one of acarbon nanotube, a carbon nanofiber, graphene, graphite, an expandedgraphite, a carbon nanopowder, a hard carbon, or a soft carbon.

An amount of the carbonaceous material in the shell may be in a range ofabout 1 to about 80 wt %, or about 2 to about 70 wt %, or about 4 toabout 60 wt %, based on the total weight of the shell, but is notlimited thereto and may be selected to provide suitable batterycharacteristics. Alternatively, an amount of the carbonaceous materialmay be about 10 wt % or less, or about 1 to about 10 wt %, or about 2 toabout 8 wt %, based on the total weight of the composite cathode activematerial.

An ion conductivity of the garnet-type oxide in the composite cathodeactive material may be 1.0×10⁻⁶ Siemens per centimeter (S/cm) or more ata temperature of 25° C. An ion conductivity of the garnet-type oxide inthe composite cathode active material may be 2.0×10⁻⁶ S/cm or more at atemperature of 25° C. An ion conductivity of the garnet-type oxide inthe composite cathode active material may be 5.0×10⁻⁶ S/cm or more at atemperature of 25° C. An ion conductivity of the garnet-type oxide inthe composite cathode active material may be 1.0×10⁻⁵ S/cm or more at atemperature of 25° C. An ion conductivity of the garnet-type oxide inthe composite cathode active material may be 2.0×10⁻⁵ S/cm or more at atemperature of 25° C. An ion conductivity of the garnet-type oxide inthe composite cathode active material may be 3.0×10⁻⁵ S/cm or more at atemperature of 25° C. The ion conductivity of the garnet-type oxide maybe an ion conductivity of lithium.

An activation energy of the garnet-type oxide of the composite cathodeactive material may be less than 0.45 electron volts (eV) at atemperature of −10° C. to 100° C. For example, an activation energy ofthe garnet-type oxide of the composite cathode active material may be0.40 eV or less at a temperature of −10° C. to 100° C. An activationenergy of the garnet-type oxide of the composite cathode active materialmay be 0.38 eV or lower at a temperature of −10° C. to 100° C. At alower activation energy, ion conductivity of a solid ion conductor maybe less sensitive to temperature and thus, within an operatingtemperature of a lithium battery, the garnet-type oxide may provideexcellent ion conductivity.

The core of the composite cathode active material may comprise a lithiumintercalatable lithium transition metal oxide, which enablesintercalation and deintercalation of lithium. For example, the core mayinclude an over-lithiated layered compound, a spinel compound, or anolivine compound.

For example, the core may comprise a compound represented by Formula 3:Li_(2−x−y−z)Me_(x+y+z)O_(2+d)  Formula 3wherein x+y+z≦1, 0<x<1, 0<y<1, 0<z<1, 0≦d≦0.1, and Me is at least one ofMn, V, Cr, Fe, Co, Ni, Zr, Re, Al, B, Ge, Ru, Sn, Ti, Nb, Mo, or Pt.

For example, the core may comprise a compound represented by Formula 4:Li_(2−x−y−z)Ma_(x)Mb_(y)Mc_(z)O_(2+d)  Formula 4wherein x+y+z≦1, 0<x<1, 0<y<1, 0<z<1, 0≦d≦0.1, and Ma, Mb, and Mc areeach independently at least one of Mn, Co, Ni, or Al.

For example, the core may comprise a compound represented by Formula 5:Li_(2−x−y−z)Ni_(x)Co_(y)Mn_(z)O_(2+d)  Formula 5wherein x+y+z≦1; 0<x<1, 0<y<1, 0<z<1, and 0≦d≦0.1. For example, inFormula 5, 0<x<0.5, 0<y<0.2, 0.3<z<0.7. For example, in Formula 5,0<x<0.3, 0<y<0.2, 0.4<z<0.6.

Also, in Formula 5, some or all of the Ni, Co, and/or Mn may besubstituted with Al.

For example, the core may include a compound represented by Formula 6:pLi₂MO₃-(1−p)LiMeO₂  Formula 6wherein 0<p<1, M is at least one of Ru, Rh, Pd, Os, Ir, Pt, Mg, Ca, Sr,Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Ni, Mn, Cr, Fe, Mg, Sr, V, or a rareearth element, and Me is at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu,Al, Mg, Zr, or B.

For example, the core may include a compound represented by Formula 7:xLi₂MO₃-yLiMeO₂-zLi_(1+d)M′_(2−d)O₄  Formula 7wherein x+y+z=1; 0<x<1, 0<y<1, 0<z<1; and 0≦d≦0.33,M is at least one of Ru, Rh, Pd, Os, Ir, Pt, Mg, Ca, Sr, Ba, Ti, Zr, Nb,Mo, W, Zn, Al, Si, Ni, Mn, Cr, Fe, Mg, Sr, V, or a rare earth element,Me is at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Mg, Zr, or B,and M′ is at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Mg, Zr, orB.

For example, the core may include a compound represented by any one ofFormulas 8 to 12:Li_(x)Co_(1−y)M_(y)O_(2−a)X_(a)  Formula 8Li_(x)Co_(1−y−z)Ni_(y)M_(z)O_(2−a)X_(a)  Formula 9Li_(x)Mn_(2−y)M_(y)O_(4−a)X_(a)  Formula 10Li_(x)Co_(2−y)M_(y)O_(4−a)X_(a)  Formula 11Li_(x)Me_(y)M_(z)PO_(4−a)X_(a)  Formula 12

In Formulas 8 to 12, 0.90≦x≦1.1, 0≦y≦0.9, 0≦z≦0.5, 1−y−z>0, 0≦a≦2, Me isat least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Mg, Zr, or B, M is atleast one of Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Ni, Mn, Cr,Fe, Mg, Sr, V, or a rare earth element, and X is at least one of O, F,S, or P.

For example, the core may include an olivine compound represented byFormula 13:Li_(x)Me_(y)M′_(z)PO_(4−d)X_(d)  Formula 13wherein 0.9≦x≦1.1, 0<y≦1, 0≦z≦1, 1.9≦x+y+z≧2.1, and 0≦d≦0.2; M is atleast one of Fe, Mn, Ni, or Co; M′ is at least one of Mg, Ca, Sr, Ba,Ti, Zr, Nb, Mo, W, Zn, Al, or Si; and X is at least one of S or F.

For example, the core may include at least one ofLi_(2−x−y−z)Ni_(x)Co_(y)Mn_(z)O₂ wherein 0<x<0.5, 0<y<0.5, and 0<z<0.9,LiCoO₂, LiFePO₄, LiFe_(1−a)Mn_(a)PO₄ wherein 0<a<1,LiNi_(0.5)Mn_(1.5)O₄, or LiMnPO₄.

A thickness of the shell of the composite cathode active material may bein a range of about 1 angstrom (Å) to about 1 micrometer (μm). Forexample, a thickness of the shell may be in a range of about 1 nanometer(nm) to about 1 μm. For example, a thickness of the shell may be in arange of about 10 nm to about 500 nm. For example, a thickness of theshell may be in a range of about 10 nm to about 100 nm. For example, athickness of the shell may be in a range of about 10 nm to about 80 nm.Within such thickness ranges of the shell, lithium batteries withimproved properties may be provided.

The core in the composite cathode active material may comprise particleshaving an average particle size of about 10 nm to about 500 μm, or 20 nmto 100 μm, or 40 nm to 10 μm. An average particle size of the core maybe in a range of about 10 nm to about 100 μm. For example, an averageparticle size of the core may be in a range of about 10 nm to about 50μm. For example, an average particle size of the core may be in a rangeof about 1 μm to about 30 μm. Within these core average particle sizeranges, lithium batteries with improved properties may be provided.

A cathode according to an embodiment may include the composite cathodeactive material.

For example, to prepare the cathode, the composite cathode activematerial, a conducting agent, a binder, and a solvent may be combined toprepare a cathode active material composition. The cathode activematerial composition may be disposed, e.g., directly coated on, analuminum current collector and dried to form a cathode plate including acathode active material layer. According to another embodiment, thecathode active material composition may be cast on a separate support,and then a film, e.g., the cathode active material layer, exfoliatedfrom the support and then laminated on the aluminum current collector toprepare a cathode plate including a cathode active material layer.

Examples of the conducting agent include at least one of a carbon, e.g.,carbon black, graphite particulate, natural graphite, artificialgraphite, acetylene black, KETJEN black, carbon fiber, and carbonnanotube; a metal, e.g., a metal powder, a metal fiber, or a metal tube,wherein the metal comprises copper, nickel, aluminum, or silver; or aconductive polymer, such as polyphenylene derivative. The conductingagent is not limited thereto, and may be any suitable conductivematerial.

The binder may comprise at least one of a vinylidenefluoride/hexafluoropropylene copolymer, polyvinylidenefluoride,polyacrylonitrile, polymethylmethacrylate, polytetrafluoroethylene(“PTFE”), or a styrene butadiene rubber-based polymer may be used, andas a solvent, at least one of N-methylpyrrolidone (“NMP”), acetone,water, or the like may be used. The solvent is not limited thereto.

In an embodiment, a plasticizer may be further added to the cathodeactive material composition to form pores in an electrode plate.

Amounts of the composite cathode active material, the conductivematerial, the binder, and the solvent may be as those used in a currentlithium battery, and can be determined by one of skill in the artwithout undue experimentation. According to the purpose and structure ofa lithium battery, one or more of the conductive material, the binder,and the solvent may be omitted.

In addition, the cathode may further include, in addition to thecomposite cathode active material, and additional cathode activematerial.

The additional cathode active material may comprise any suitablelithium-containing metal oxide that is used in the art. For example, atleast one composite oxide of lithium and at least one metal of cobalt,manganese, or nickel may be used. The composite oxide may be representedby one of Li_(a)A_(1−b)Z_(b)D₂ (wherein 0.90≦a≦1, and 0≦b≦0.5);Li_(a)E_(1−b)Z_(b)O_(2−c)D_(c) (wherein 0.90≦a≦1, 0≦b≦0.5, and0≦c≦0.05); LiE_(2−b)Z_(b)O_(4−c)D_(c) (wherein 0≦b≦0.5, and 0≦c≦0.05);Li_(a)Ni_(1−b−c)Co_(b)Z_(c)D_(a) (wherein 0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05,and 0<a<2); Li_(a)Ni_(1−b−c)Co_(b)Z_(c)O_(2−a)X_(a) (wherein 0.90≦a≦1,0≦b≦0.5, 0≦c≦0.05, and 0<a<2); Li_(a)Ni_(1−b−c)Co_(b)Z_(c)O_(2−a)X₂(wherein 0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05, and 0<a<2);Li_(a)Ni_(1−b−c)Mn_(b)Z_(c)D_(a) (wherein 0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05,and 0<a<2); Li_(a)Ni_(1−b−c)Mn_(b)Z_(c)O_(2−a)X_(a) (wherein 0.90≦a≦1,0≦b≦0.5, 0≦c≦0.05, and 0<a<2); Li_(a)Ni_(1−b−c)Mn_(b)Z_(c)O_(2−a)X₂(wherein 0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05, and 0<a<2);Li_(a)Ni_(b)E_(c)G_(d)O₂ (wherein 0.90≦a≦1, 0≦b≦0.9, 0≦c≦0.5, and0.001≦d≦0.1); Li_(a)Ni_(b)Co_(c)Mn_(d)GeO₂ (wherein 0.90≦a≦1, 0≦b≦0.9,0≦c≦0.5, 0≦d≦0.5, and 0.001≦e≦0.1); Li_(a)NiG_(b)O₂ (wherein 0.90≦a≦1,and 0.001≦b≦0.1); Li_(a)CoG_(b)O₂ (wherein 0.90≦a≦1, and 0.001≦b≦0.1);Li_(a)MnG_(b)O₂ (wherein 0.90≦a≦1, and 0.001≦b≦0.1); Li_(a)Mn₂G_(b)O₄(wherein 0.90≦a≦1, and 0.001≦b≦0.1); QO₂; QS₂; LiQS₂; V₂O₅; LIV₂O₅;LiQ′O₂; LiNiVO₄; Li_((3−f))J₂(PO₄)₃(0≦f≦2); Li_((3−f))Fe₂(PO₄)₃(0≦f≦2);and LiFePO₄:

wherein

A is at least one of Ni, Co, or Mn;

Z is at least one of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, or a rare-earthelement;

D is at least one of O, F, S, or P;

E is at least one of Co, or Mn;

X is at least one of F, S, or P;

G is at least one of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, or V;

Q is at least one of Ti, Mo, or Mn;

I is at least one of Cr, V, Fe, Sc, or Y; and

J is at least one of V, Cr, Mn, Co, Ni, or Cu.

For example, LiCoO₂, LiMn_(x)O_(2x) (e.g., wherein x=1 or 2),LiNi_(1−x)Mn_(x)O_(2x) (0<x<1), LiNi_(1−x−y)Co_(x)Mn_(y)O₂ (0≦x≦0.5,0≦y≦0.5), FePO₄, or the like may be used.

These compounds may have a coating layer on their surfaces, or thesecompounds may be combined with a compound having a coating layer. Thecoating layer may include an oxide, a hydroxide, an oxyhydroxide, anoxycarbonate, or a hydroxycarbonate. The coating layer may comprise anamorphous or crystalline compound. The coating layer may comprise acompound comprising at least one of Mg, Al, Co, K, Na, Ca, Si, Ti, V,Sn, Ge, Ga, B, As, or Zr. The coating layer may be formed by using anysuitable coating methods, wherein suitable coating methods are thosewhich do not adversely affect desirable properties of the cathode activematerial. Suitable coating methods may include, for example, spraycoating, immersion, or the like. Details of suitable coating methods maybe determined by one of skill in the art without undue experimentation,and thus are not described in further detail herein.

A lithium battery according to an embodiment includes a cathodeincluding the composite cathode active material. The lithium battery maybe manufactured by the following method.

First, a cathode is manufactured by the cathode manufacturing methoddescribed above.

Then, an anode may be manufactured by the following manner. The anodemay be manufactured in the same manner as used to manufacture thecathode, except that an anode active material is used instead of thecomposite cathode active material. In addition, a conductive material, abinder, and a solvent used in an anode active material composition maybe the same as those used in the cathode.

For example, an anode active material, a conducting agent, a binder, anda solvent may be combined to prepare an anode active materialcomposition, and the anode active material composition may be directlydisposed on, e.g., coated on, a copper current collector to manufacturean anode plate. According to another embodiment, the anode activematerial composition is cast on a separate support, and an anode activematerial film exfoliated from the support and laminated on a coppercurrent collector to manufacture an anode plate.

In addition, the anode active material may comprise any suitablematerial that is used as an anode active material for a lithium batteryin the art. For example, the anode active material may include at leastone of lithium metal, a lithium-alloyable metal, a transition metaloxide, a non-transition metal oxide, or a carbonaceous material.

For example, the lithium-alloyable metal may comprise Si, Sn, Al, Ge,Pb, Bi, Sb, a Si—Y alloy (wherein Y is at least one of an alkali metal,alkaline earth metal, a Group 13 element, a Group 14 element, atransition metal, or a rare-earth element, and Y is not Si), or a Sn—Yalloy (wherein Y is at least one of an alkali metal, an alkaline earthmetal, a Group 13 element, a Group 14 element, a transition metal, or arare-earth element, and Y is not Sn). The element Y may comprise atleast one of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db,Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag,Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, or Po.

For example, the transition metal oxide may comprise at least one oflithium titanium oxide, vanadium oxide, or lithium vanadium oxide.

For example, the transition metal oxide may comprise at least one ofSnO₂, SiO_(x) (wherein 0<x<2), or the like.

The carbonaceous material may comprise at least one of a crystallinecarbon or an amorphous carbon. The crystalline carbon may comprise atleast one of a natural or artificial graphite that is amorphous,tabular, flake, circular, or fibrous, and the amorphous carbon may be asoft carbon (e.g., cold calcined carbon) or a hard carbon, meso-phasepitch carbide, or a calcined cork.

Amounts of the anode active material, the conductive material, thebinder, and the solvent may be those used in the art, and can bedetermined by one of skill in the art without undue experimentation.

Then, a separator which is to be disposed between the cathode and theanode is prepared. As a separator, any suitable material that is used inthe art may be used. For example, the separator may have a lowresistance to movement of electrolytic ions and excellentelectrolyte-retaining capabilities. For example, at least one of glassfiber, polyester, Teflon, polyethylene, polypropylene, orpolytetrafluoroethylene (“PTFE”), each of which may be in a woven- ornon-woven form, may be used. In detail, a separator for a lithium ionbattery may be a rollable separator formed of polyethylene orpolypropylene, and a separator for a lithium ion polymer battery may bea separator having excellent organic electrolyte-retaining capabilities.For example, the separator may be prepared by using the followingmethod.

A separator composition may be prepared by mixing a polymer resin, afiller, and a solvent. The separator composition may be directly coatedor dried on an electrode to complete the formation of the separator.Alternatively, the separator composition may be cast on a separatesupport and then a film separated from the support is laminated on anelectrode, thereby completing the formation of the separator.

A polymer resin used in preparing the separator may not be particularlylimited, and any suitable material used for a binder of an electrodeplate may be used. For example, at least one of a vinylidenefluoride/hexafluoropropylene copolymer, polyvinylidenefluoride (“PVDF”),polyacrylonitrile, or polymethylmethacrylate.

Then, an electrolyte is prepared.

For example, the electrolyte may be an organic electrolyte. According toanother embodiment, the electrolyte may be a solid, e.g., an inorganicmaterial. For example, boron oxide, lithium oxynitride, or the like maybe used, but the electrolyte may not be limited thereto, and theelectrolyte may be any suitable materials that is used as a solidelectrolyte in the art. The solid electrolyte may be formed on an anodeby, for example, sputtering.

For example, an organic electrolyte may be prepared. The organicelectrolyte may be prepared by dissolving a lithium salt in an organicsolvent.

The organic solvent may comprise any suitable material that is used asan organic solvent in the art. For example, the organic solvent maycomprise at least one of propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethylcarbonate, methylethyl carbonate, methylpropyl carbonate, ethylpropylcarbonate, methylisopropyl carbonate, dipropyl carbonate, dibutylcarbonate, benzonitrile, acetonitrile, tetrahydrofuran,2-methyltetrahydrofurane, γ-butyrolactone, dioxolane, 4-methyldioxolane,N,N-dimethylformamide, dimethylacetamide, dimethylsulfoxide, dioxane,1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene,nitrobenzene, diethyleneglycol, or dimethylether.

The lithium salt may comprise any suitable lithium salt used in the art.For example, the lithium salt may comprise at least one of LiPF₆, LiBF₄,LiSbF₆, LiAsF₆, LiClO₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, LiC₄F₉SO₃, LiAlO₂,LiAlCl₄, LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) (wherein x and y arenatural numbers), LiCl, or LiI.

As shown in FIG. 5, a lithium battery 1 includes a cathode 3, an anode2, and a separator 4. The cathode 3, the anode 2, and the separator 4are wound or folded to be placed in a battery case 5. Then, an organicelectrolyte is disposed in the batter case 5, and then sealed with a capassembly 6 to complete the manufacturing of the lithium battery 1. Thebattery case 5 may be a circular case, a rectangular case, or athin-film type case. For example, the lithium battery may be a largethin film-type battery. The lithium battery may be a lithium ionbattery.

The separator 4 may be disposed between the cathode 3 and the anode 2 tocomplete the manufacturing of a battery assembly. When batteryassemblies are stacked in a bi-cell structure, the resulting structureis immersed in an organic electrolyte, and the obtained assembly ishoused in a pouch, followed by being sealed to complete themanufacturing of a lithium ion polymer battery.

In addition, battery assemblies may be stacked to form a battery pack,and the battery pack may be used in various applications to provide highcapacity and high performance. For example, the battery pack may be usedin a notebook, a smart phone, an electric vehicle, or the like.

In addition, the lithium battery may be used in an electric vehicle(“EV”) due to its lifetime characteristics and high-ratecharacteristics. For example, the lithium battery may be used in aplug-in hybrid electric vehicle (“PHEV”). In addition, the lithiumbattery may be used in applications requiring a great amount of electricpower. For example, the lithium battery may be used in an electricbicycle, an electric tool, or the like.

A method of preparing a composite cathode active material, according toan embodiment, includes forming a shell comprising the garnet-type oxideon a core particle comprising a lithium intercalatable material.

For example, the shell may be formed by a dry coating method.

When the shell is formed by a dry coating method, the method maycomprise contacting a lithium intercalatable material for a core, whichis an electrode active material enabling intercalation anddeintercalation of lithium, and a garnet-type oxide; and forming ashell, e.g., a coating, comprising the garnet-type oxide on the core bythe dry coating method.

The dry coating method may comprise a method of forming a shell (or asurface-treated layer) by applying mechanical energy to a mixtureincluding a core particle including an electrode active material and alithium metal oxide particle, without use of a solvent.

The dry coating method may comprise, for example,

a) a method which comprises disposing, e.g., contacting and/orattaching, a powder of a covering material, for example a garnet-typeoxide powder, and a surface of a particle of a lithium intercalatablematerial with a low speed ball mill, e.g., one operating at about 200 toabout 2000 revolutions per minute (“RPM”), and simultaneously coheringthe attached particles of the lithium intercalatable material and thegarnet-type oxide to each other to form a shell of the garnet-type oxideon a core of the lithium intercalatable material,

b) a method comprising confining and/or attaching covering materialparticles comprising the garnet-type oxide on a surface of particles ofthe lithium intercalatable material for the core by rotation of agrinding media and/or a rotator disposed in an apparatus, e.g., a KADYmill, and simultaneously mechanically binding the covering materialparticles on the core particle by stresses or binding the particles bysoftening or fusing a shell of the covering material particles, e.g. thegarnet-type oxide, on the core particle by a heat produced by thestresses, or

c) a method which comprises fusing a portion or the entire shell and thecore by performing a heat treatment on the core covered with the shell,which may be formed according to the foregoing methods a) and/or b) andthen cooling. The method is not limited thereto, and any suitable drycoating process used in the art may be used.

For example, the dry coating method may be any suitable methodcomprising a ball mill method, a low-speed ball mill method, ahigh-speed ball mill method, a hybridization method, or a mechanofusionmethod. In the low-speed ball mill method, a ball mill operating atabout 200 to about 2000 RPM may be used. In the high-speed ball millmethod, a ball mill operating at about 2000 to about 10,000 RPM may beused. For example, the dry coating method may be a mechanofusion method.

According to the mechanofusion method, a mixture is provided into avessel that is rotating and then, due to a centrifugal force, themixture is fixed on an inner wall of the vessel and then, the mixture iscompressed in a gap between the inner wall of the vessel and an arm headnear the inner wall of the vessel. The mechanofusion method correspondsto the method b).

The dry coating method may further include heat treating the resultingcomposition including the shell after the formation of the shell. Due tothe heat treatment, the shell may be more firmly bonded and/or morestable than before the heat treatment. A heat treatment condition thatmay fuse a portion or the entire shell may be available.

In the method, an amount of the garnet-type oxide may be about 2 wt % orless, based on the total weight of the core and the garnet-type oxide.For example, an amount of the garnet-type oxide may be in a range ofgreater than 0 to about 2 wt %, based on the total weight of the coreand the garnet-type oxide. For example, the amount of the garnet-typeoxide may be greater than 0 to about 1.5 wt %, based on the total weightof the core and the garnet-type oxide. For example, the amount of thegarnet-type oxide may be greater than 0 to about 1.0 wt %, based on thetotal weight of the core and the garnet-type oxide.

In the method, the shell may be formed by using, in addition to thegarnet-type oxide, a carbonaceous material. For example, thecarbonaceous material may comprise at least one of a carbon nanotube, acarbon nanofiber, graphene, an expanded graphite, a carbon nanopowder, ahard carbon, and a soft carbon. An amount of the carbonaceous materialmay be in a range of 1 to 300 parts by weight, based on 100 parts byweight of the garnet-type oxide.

Hereinafter, embodiments are described in further detail with referenceto Examples and Comparative Examples. The Examples are presented hereinfor illustrative purpose only, and do not limit the scope of the presentdisclosure.

EXAMPLES Preparation of Garnet-Type Oxide Preparation Example 1

LiOH, which is a Li precursor, La₂O₃, which is a La precursor, and ZrO₂,which is a Zr precursor, were used as starting materials and combined ina stoichiometry to obtain Li₇La₃Zr₂O₁₂ to form a mixture.

The mixture was mixed and milled in isopropyl alcohol using a planetaryball mill (400 RPM, zirconia oxide ball) for 6 hours. The milled andmixed powder was placed in an alumina melting pot, and calcined in airat a temperature of 900° C. for 12 hours.

To compensate for loss of Li, excess LiOH was added, in an amount of 10wt % with respect to an amount of Li contained in the final productcomposition, to the calcined powder.

The resulting mixture, including the lithium hydroxide, was mixed andmilled for 6 hours in isopropyl alcohol using a planetary ball mill (500RPM, zirconia oxide ball). The calcined powder was molded in the form ofpellet or thin film or was not molded, and then calcined in air at atemperature of 1100° C. for 20 hours to complete the preparation of asolid ion conductor.

Subsequently, the Li₇La₂Zr₃O₁₂ was milled using a ball mill for 24 hoursto prepare Li₇La₂Zr₃O₁₂ particles having an average particle size ofabout 100 nm.

Preparation Example 2

A solid ion conductor was prepared in the same manner as in PreparationExample 1, except that a stoichiometric ratio of the starting materialswas changed to obtain Li_(6.75)La₃(Zr_(1.75)Nb_(0.25))O₁₂, andadditionally, NbO₂ was used.

Preparation Example 3

A solid ion conductor was prepared in the same manner as in PreparationExample 1, except that a stoichiometric ratio of the starting materialswas changed to obtain Li_(7.5)Rb_(0.25)La_(2.75)Zr₂O₁₂, andadditionally, Rb₂CO₃ was used.

Preparation Example 4

A solid ion conductor was prepared in the same manner as in PreparationExample 1, except that a stoichiometric ratio of the starting materialswas changed to obtain Li_(7.5)Rb_(0.5)La_(2.75)Zr₂O₁₂, and additionally,Rb₂CO₃ was used.

Preparation Example 5

A solid ion conductor was prepared in the same manner as in PreparationExample 4, except that a stoichiometric ratio of the starting materialswas changed to obtain Li₉RbLa₂Zr₂O₁₂.

Preparation Example 6

A solid ion conductor was prepared in the same manner as in PreparationExample 4, except that a stoichiometric ratio of the starting materialswas changed to obtain Li_(7.125)Rb_(0.0625)La_(2.9375)Zr₂O₁₂.

Preparation Example 7

A solid ion conductor was prepared in the same manner as in PreparationExample 1, except that a stoichiometric ratio of the starting materialswas changed to obtain Li₆SrLa₂Ta₂O₁₂, and additionally, SrCO₃ was used.

Preparation Example 8

A solid ion conductor was prepared in the same manner as in PreparationExample 1, except that a stoichiometric ratio of the starting materialswas changed to obtain Li_(7.125)K_(0.0625)La_(2.9375)Zr₂O₁₂, andadditionally, KOH was used.

Preparation of Composite Cathode Active Material Example 1

0.2 parts by weight of Li₇La₂Zr₃O₁₂ particles prepared according toPreparation Example 1 and 100 parts by weight ofLi_(1.18)Ni_(0.17)Co_(0.1)Mn_(0.56)O₂ powder having an average particlesize of 10 μm were combined to form a mixture. The mixture was placed ina dry surface treatment apparatus (Hosokawa Micron Corporation, Japan,Mechanofusion device, Nobilta-mini) and then, treated for 20 minutes at3000 RPM to prepare a composite cathode active material in which a shellincluding Li₇La₂Zr₃O₁₂ was formed on aLi_(1.18)Ni_(0.17)Co_(0.1)Mn_(0.56)O₂ core. The prepared compositecathode active material is shown in FIGS. 1A to 1C.

Example 2

A composite cathode active material was prepared in the same manner asin Example 1, except that an amount of the Li₇La₂Zr₃O₁₂ was 0.5 parts byweight.

Example 3

A composite cathode active material was prepared in the same manner asin Example 1, except that an amount of the Li₇La₂Zr₃O₁₂ particles was1.0 part by weight.

Example 4

A composite cathode active material was prepared in the same manner asin Example 3, except that 1.0 part by weight of multi-walled carbonnanotube (MWCNT, e-nanotech) was used instead of 1.0 part by weight ofthe Li₇La₂Zr₃O₁₂ particles.

Example 5

A composite cathode active material was prepared in the same manner asin Example 3, except that 1.0 part by weight of a multi-walled carbonnanotube (MWCNT, e-nanotech) and 0.5 parts by weight of Li₇La₂Zr₃O₁₂particles were used instead of 1.0 part by weight of Li₇La₂Zr₃O₁₂particles.

Examples 6 to 12

A composite cathode active material was prepared in the same manner asin Example 1, except that the garnet-type oxides (a solid ion conductor)prepared according to Preparation Examples 2 to 8 were used.

Comparative Example 1

Li_(1.18)Ni_(0.17)Co_(0.1)Mn_(0.56)O₂ powder having an average particlesize of 10 μm was used as a cathode active material without the formingof a surface-treated layer.

Comparative Example 2

A composite cathode active material was prepared in the same manner asin Example 1, except that an amount of Li₇La₂Zr₃O₁₂ particle was 2.0parts by weight.

Comparative Example 3

0.2 parts by weight of Li₇La₂Zr₃O₁₂ particles prepared according toPreparation Example 1 and 100 parts by weight ofLi_(1.18)Ni_(0.17)Co_(0.1)Mn_(0.56)O₂ powder having an average particlesize of 10 μm were simply mixed to prepare a composite cathode activematerial.

Preparation of Cathode Example 13

The composite cathode active material prepared according to Example 1, acarbon conducting agent (Denka Black), and polyvinylidenefluoride(“PVdF”) were combined at a weight ratio of 92:4:4 to form a mixture,and then, the mixture was mixed with N-methylpyrrolidone (“NMP”) in anagate mortar to prepare slurry. The slurry was bar-coated on a 15μm-thick aluminum current collector and then dried at room temperature,then dried in a vacuum at a temperature of 120° C., and then, pressedand punched to manufacture a 55 μm-thick cathode plate.

Examples 7 to 24

Cathode plates were prepared in the same manner as in Example 6, exceptthat the composite cathode active materials of Examples 2 to 12 wereprepared.

Comparative Examples 4 to 6

Cathode plates were prepared in the same manner as in Example 6, exceptthat the cathode active materials of Comparative Examples 1 to 3 wereprepared.

Comparative Example 7

A cathode plate was prepared in the same manner as in Example 6 exceptthat the cathode active material of Comparative Example 1 was used, andthen, a Li₇La₂Zr₃O₁₂ shell was formed on a cathode active material layeron the cathode plate. An amount of the garnet-type oxide layer was in arange of 1 part by weight, based on 100 parts by weight of the cathodeactive material.

In detail, an NMP solution containing 1 part by weight of Li₇La₂Zr₃O₁₂was dropped onto a cathode active material layer of the cathode plate,and then, dried at a temperature of 120° C. in an oven to form aLi₇La₂Zr₃O₁₂ shell.

Manufacture of a Lithium Battery Example 25

A coin cell was manufactured using the cathode plate prepared accordingto Example 13, a lithium metal a counter electrode, a PTFE separator,and as an electrolyte a solution in which 1.3 molar (M) LiPF₆ wasdissolved in a solution of ethylene carbonate (“EC”), diethyl carbonate(“DEC”), and ethyl methyl carbonate (“EMC”) at a volumetric ratio of3:5:2.

Examples 26 to 36

Coin cells were manufactured in the same manner as in Example 25, exceptthat the cathode plates prepared according to Examples 12 to 24 wereused.

Comparative Examples 8 to 11

Coin cells were manufactured in the same manner as in Example 25, exceptthat the cathode plates prepared according to Comparative Examples 4 to7 were used.

Evaluation Example 1 XRD Analysis

X-ray diffraction (“XRD”) analysis was performed on Li₇La₂Zr₃O₁₂particles prepared according to Preparation Example 1, and resultsthereof are shown in FIG. 2. In the XRD Cu—Kα radiation was used.

As shown in FIG. 2, the peak of the garnet-type oxide was sharp, whichmeans the garnet-type oxide has high crystallinity. The garnet-typeoxide retained high crystallinity even after milling.

Evaluation Example 2 ICP-AES Analysis

Inductively coupled plasma-atomic emission spectrometry (“ICP-AES”)analysis was performed on surfaces of the composite cathode activematerials prepared according to Examples 1 to 3 and Comparative Example1, and the obtained surface composite analysis results are shown inTable 1.

TABLE 1 Li Mn Co Ni Zr La [% wt/ [% wt/ [% wt/ [% wt/ [% wt/ [% wt/ wt]wt] wt] wt] wt] wt] Example 1 1.403 0.603 0.198 0.199 0.00059 0.00062Example 2 1.403 0.604 0.200 0.202 0.00129 0.00139 Example 3 1.403 0.6000.200 0.201 0.00199 0.00262 Comparative 1.437 0.603 0.198 0.199 — —Example 1

As shown in Table 1, in the surfaces of the composite cathode activematerials of Examples 1 to 3, La content and Zr content are increased,and in the case of Comparative Example 1, La and Zr were not detected.

Evaluation Example 2 TOF-SIMS Analysis

Time-of-flight secondary ion mass spectrometry (“TOF-SIMS”) wasperformed on surfaces of the composite cathode active materials preparedaccording to Examples 1 to 3 and Comparative Examples 1 and 3, and theconcentration depth profiles of the respective components from thesurface to the inside are shown in FIGS. 3A to 3F.

As shown in FIG. 3A, a concentration of LaO on surfaces of the compositecathode active materials of Examples 1 to 3 was higher than that ofComparative Example 3 in which 1 wt % of garnet-type oxide was simplymixed. Accordingly, it was confirmed that a shell was formed on surfacesof the composite cathode active materials of Examples 1 to 3.

Evaluation Example 3 High-Rate Characteristics Evaluation

During a 1^(st) cycle, the coin cells manufactured according to Examples25 to 36 and Comparative Examples 8 to 11 were constant-current chargedat a rate of 0.1 C until the voltage reached 4.6 V and then, the coincells were constant-current discharged at a rate of 0.1 C until thevoltage reached 2.5 V.

During a 2^(nd) cycle, the coin cells were constant-current charged at arate of 0.5 C until the voltage reached 4.6 V, and then, while thevoltage maintained at 4.6 V, the coin cells were constant-voltagecharged until the current reached 0.05 C and then, at a rate of 0.2 C,the coin cells were constant-current discharged until the voltagereached 2.5 V.

During a 3^(rd) cycle, the coin cells were constant-current charged at arate of 0.5 C until the voltage reached 4.6 V, and then, while thevoltage maintained at 4.6 V, the coin cells were constant-voltagecharged until the current reached 0.05 C and then, at a rate of 1.0 C,the coin cells were constant-current discharged until the voltagereached 2.5 V.

During a 4^(th) cycle, the coin cells were constant-current charged at arate of 0.5 C until the voltage reached 4.6 V, and then, while thevoltage maintained at 4.6 V, the coin cells were constant-voltagecharged until the current reached 0.05 C and then, at a rate of 2.0 C,the coin cells were constant-current discharged until the voltagereached 2.5 V.

Some of charging and discharging results are shown in Table 2 below.Initial coulombic efficiency and high-rate characteristics arerespectively defined as shown Equations 1 and 2 below.Initial coulombic efficiency [%]=[discharging capacity in 1^(st)cycle/charging capacity in 1^(th) cycle]×100  Equation 12C capacity retention ratio [%]=[discharging capacity in 4^(th)cycle/discharging capacity in 2^(nd) cycle]×100  Equation 2

TABLE 2 Initial charging and 2 C capacity retention dischargingefficiency ratio [%] [%] Example 25 90.6 81.9 Example 26 90.7 82.1Example 27 90.4 80.8 Example 28 90.9 83.3 Example 29 91.3 83.7Comparative 89.8 74.2 Example 8 Comparative 86.7 65.9 Example 9Comparative 88.0 77.2 Example 10 Comparative 89.7 77.9 Example 11

As shown in Table 2, the coin cells of Examples 25 to 29 had higherinitial charging and discharging efficiency and better high-ratecharacteristics than the coin cells of Comparative Example 8 to 11.

Evaluation Example 7 Lifespan Characteristics Evaluation

The coin cells manufactured according to Examples 25 to 36 andComparative Examples 8 and 11 were constant-current charged anddischarged at a temperature of 45° C. in a voltage range of 2.5 to 4.6 Vwith respect to lithium metal at a rate of 1 C rate for 50 times. Acapacity retention ratio in the 50^(th) cycle is indicated as Equation 3below. The capacity retention ratio in the 50^(th) cycle is shown inTable 3 and FIG. 3.Capacity retention ratio in 50^(th) cycle [%]=[discharging capacity in50^(th) cycle/discharging capacity in 1^(st) cycle]×100  Equation 3

TABLE 3 Capacity retention rate in 50th cycle [%] Example 25 88.75Example 26 89.37 Example 27 88.51 Comparative Example 8 85.7 ComparativeExample 84.09 11

As shown in Table 3 and FIG. 4, the coin cells manufactured according toExamples 25 to 27 showed substantially improved lifespan characteristicscompared to the coin cells manufactured according to ComparativeExamples 8 and 11.

According to an embodiment, due to the inclusion of a material thatenables intercalation and deintercalation of lithium and a garnet-typeoxide in a composite cathode active material, high-rate characteristicsand lifespan characteristics of a lithium battery including thecomposite cathode active material may improve.

It should be understood that the exemplary embodiments described thereinshould be considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments.

What is claimed is:
 1. A composite cathode active material comprising: acore and a shell disposed on at least a portion of the core, wherein thecore comprises a lithium intercalatable material and the shell comprisesa garnet oxide, wherein an amount of the garnet oxide is less than 1.9weight percent, based on a total weight of the composite cathode activematerial, wherein the core comprises a compound represented by Formula4:Li_(2−x−y−z)Ma_(x)Mb_(y)Mc_(z)O_(2+d)  Formula 4 wherein x+y+z≦1; 0<x<1,0<y<1, 0<z<1, and 0≦d≦0.1, and Ma, Mb, and Mc are each independently atleast one metal of Mn, Co, Ni, or Al.
 2. The composite cathode activematerial of claim 1, wherein the shell and the core form amechanochemical bond.
 3. The composite cathode active material of claim1, wherein the garnet oxide is represented by Formula 1 below:L_(5+x)E₃(Me_(z)M_(2−z))O_(d)  Formula 1 wherein L comprises at leastone of a monovalent cation and a bivalent cation, wherein L comprisesLi, E comprises a monovalent cation and a trivalent cation, Me and Meach independently comprise a trivalent, a 4-valent, a 5-valent, or a6-valent cation, 0<x≦3, 0≦z≦2, and 0<d≦12, O is optionally substitutedwith at least one of a 5-valent, a 6-valent, or a 7-valent anion.
 4. Thecomposite cathode active material of claim 1, wherein the garnet oxideis represented by Formula 2:Li_(5+x)La₃(Zr_(z)A_(2−z))O₁₂  Formula 2 wherein A comprises at leastone of Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, Ga, or Ge, 0<x≦3, and 0≦z≦2. 5.The composite cathode active material of claim 1, wherein the garnetoxide comprises at least one of Li₇La₃Zr₂O₁₂, Li_(6.75)La₃(Zr_(1.75),Nb_(0.25))O₁₂, Li_(7.5)Rb_(0.25)La_(2.75)Zr₂O₁₂,Li₈Rb_(0.5)La_(2.5)Zr₂O₁₂, Li₉RbLa₂Zr₂O₁₂,Li_(7.125)Rb_(0.0625)La_(2.9375)Zr₂O₁₂, Li₆SrLa₂Ta₂O₁₂, orLi_(7.125)K_(0.0625)La_(2.9375)Zr₂O₁₂.
 6. The composite cathode activematerial of claim 1, wherein the shell further comprises a carbonaceousmaterial.
 7. The composite cathode active material of claim 6, whereinthe carbonaceous material comprises at least one of a carbon nanotube, acarbon nanofiber, graphene, graphite, an expanded graphite, a carbonnanopowder, a hard carbon, or a soft carbon.
 8. The composite cathodeactive material of claim 1, wherein the core comprises a compoundrepresented by Formula 5:Li_(2−x−y−z)Ni_(x)Co_(y)Mn_(z)O_(2+d)  Formula 5 wherein x+y+z≦1; 0<x<1,0<y<1, 0<z<1, and 0≦d≦0.1.
 9. A cathode comprising the composite cathodeactive material of claim
 1. 10. A lithium battery comprising the cathodeof claim
 9. 11. A method of preparing a composite cathode activematerial, the method comprising: contacting a lithium intercalatablematerial and a garnet oxide to form a shell comprising the garnet oxidedisposed on a core comprising the lithium intercalatable material toprepare the composite cathode active material, wherein an amount of thegarnet oxide is less than 1.9 weight percent, based on a total weight ofthe composite cathode active material, wherein the core comprises acompound represented by Formula 4:Li_(2−x−y−z)Ma_(x)Mb_(y)Mc_(z)O_(2+d)  Formula 4 wherein x+y+z≦1, 0<x<1,0<y<1, 0<z<1, and 0≦d≦0.1, and Ma, Mb, and Mc are each independently atleast one metal of Mn, Co, Ni, or Al.
 12. The method of claim 11,wherein the contacting comprises a dry coating method.
 13. The method ofclaim 12, wherein the dry coating method comprises at least one of ballmilling, a hybridization method, or a mechanofusion method.
 14. Thecomposite cathode active material of claim 1, wherein the amount of thegarnet oxide is greater than 0 to about 1.5 wt %.
 15. The compositecathode active material of claim 1, wherein the amount of the garnetoxide is greater than 0 to about 1.0 wt %.